Nearly every company on this map traces to a single decision made in Pasadena in 1930.
That year the Guggenheim family paid to bring Theodore von Kármán to Caltech to run its aeronautics lab. His graduate students, a crew known on campus as the Suicide Squad, lit their first liquid rocket motor in a dry riverbed north of the Rose Bowl on Halloween 1936. That test site became JPL.
The aircraft industry stacked in around it. Lockheed, Douglas, Northrop, and Hughes built planes across the same basin through WWII and the Cold War. Each generation of engineers trained here, then trained the next batch, then sent their kids to the same schools.
The talent never left. That is the whole story of this map.
SpaceX headquarters sits at 1 Rocket Road in Hawthorne, inside the old Northrop plant that built aircraft on that spot for 70 years. The same building once turned out 747 fuselages. Elon put the rocket factory there because the workforce was already standing in the parking lot.
You can move a headquarters with a single post. No one has figured out how to move tens of thousands of aerospace engineers and the knowledge sitting in their heads. When the SpaceX HQ move to Texas got announced, this map barely lost a dot.
The startups are new. The cluster feeding them is almost a century old, and it compounds every year a fresh graduate walks out of Caltech or USC into the company next door.